Modeling and Analysis of Linear Complexions in Metal Alloys

Rupert Lab - UC Irvine

January 2022 - March 2023

Mentored by Divya Singh and Pulkit Garg

Introduction

During my time in the Rupert Lab, I was tasked with running simulations to better understand how metals are strengthened by their defects. While solid solution strengthening is a type of alloying known to improve the strength of the metal, we wanted to more closely examine and model precipitation hardening, in which the solute of an alloy forms bulk precipitates that hinder the movement of the dislocation. Overall, the goal of the simulations was to find the minimum stress at which the dislocation in a nickel-aluminum alloy would completely detach from linear complexions to further analyze the effects of such formations of atomic structures on the overall strength of metal alloys.

Methods and Visualization

Using Large-scale/Molecular Massively Parallel Simulator (LAMMPS), I ran Monte Carlo/molecular dynamics simulations under constant temperature at 300K, changing the pressure applied to the sample in each simulation to approximate the critically-resolved shear stress (CRSS) near individual complexions in the sample.

Isolated the complexion of interest by cutting the sample along its length and maintaining the periodic boundaries
Duplicated the complexion of interest at varying distances to analyze how the CRSS would change with smaller or larger distances between complexions
Extracted dump files for visualization in Open Visualization Tool (OVITO), where we performed a dislocation analysis and Polyhedral Template Matching to identify local chemical ordering and better view whether the complexion of interest had completely detached from the dislocation at 1 picosecond (ps) time intervals

Simulation run on circled linear complexion

Circled linear complexion when duplicated at a distance of 132 Angstroms after 1 ps and 8 ps, respectively

Linear complexion when duplicated at a distance of 14 Angstroms after 1 ps, 7 ps, and 8 ps, respectively

Conclusions

From these simulations, we concluded that the formation of a linear complexion along a dislocation strengthens the dislocation in comparison to solid solution dislocation strengthening, with the strengthening effect dependent on the complexion type. Linear complexions physically prevent the dislocation from shifting or moving in areas where the complexion is present.

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